Positive electrode material, positive electrode sheet, and secondary battery

Abstract

The present application provides a positive electrode material, a positive electrode sheet, and a secondary battery. The length-to-diameter ratio X / Y of particles in the positive electrode material satisfies: 1≤X / Y≤1.6, wherein X is the length of the longest straight edge of a single particle, and Y is the length of the straight edge perpendicular to the midpoint position of the longest straight edge. After compaction under a pressure of 6 T, particles below 1 μm in the positive electrode material have a volume proportion ranging from 2% to 4%. According to the present application, by controlling the length-to-diameter ratio of the particles and the content of micro powder in the positive electrode material, it is ensured that the battery has a good capacity while improving the long-term cycle performance, high-temperature storage performance, and gas production performance of the battery.

Description

Positive electrode material, positive electrode sheet and secondary battery

[0001] This application claims priority to Chinese patent application 202411934832.0, filed on December 26, 2024. The entire contents of the aforementioned Chinese patent application are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery cathode material technology, specifically to a cathode material, a cathode sheet, and a secondary battery. Background Technology

[0003] Ternary cathode materials are among the most widely used cathode materials in lithium-ion batteries, possessing advantages such as high discharge specific capacity and high energy density, while their production cost is significantly lower than that of LiCoO2. Among numerous cathode materials, ternary cathode materials have become the most widely used in the lithium-ion battery field due to their high specific capacity and high voltage platform. However, existing cathode materials exhibit poor high-temperature storage performance and low energy density, necessitating improvements. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above defects, it is necessary to provide a cathode material.

[0005] In addition, it is necessary to provide a method for preparing the aforementioned positive electrode material, as well as a positive electrode sheet and a secondary battery using the aforementioned positive electrode material.

[0006] In a first aspect, embodiments of this application provide a cathode material in which the average aspect ratio X / Y of the particles in the cathode material, as shown in the scanning electron microscope image, satisfies: 1≤X / Y≤1.6, where X is the length of the longest straight side of a single particle, and Y is the length of the straight side perpendicular to the midpoint of the longest straight side. After compaction under 6T pressure, the cathode material is characterized by laser particle size distribution, and the volume percentage of particles smaller than 1μm in the cathode material is 2% to 4%.

[0007] Thirdly, embodiments of this application provide a positive electrode sheet, including the positive electrode material as described above.

[0008] Fourthly, embodiments of this application provide a secondary battery, including the positive electrode material or the positive electrode sheet as described above.

[0009] The cathode material provided in this application aims to improve the long-term cycle performance, high-temperature storage performance, and gas generation performance of the cathode material by controlling the aspect ratio of the particles and the volume ratio of particles smaller than 1μm in the cathode material, while ensuring that the cathode material has good capacity, thereby achieving an improvement in the overall performance of the cathode material. Attached Figure Description

[0010] Figure 1 is a cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application during charging.

[0011] Figure 2 is a cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application during discharge.

[0012] Figure 3 is a scanning electron microscope (SEM) image of the cathode material of Example 1 of this application.

[0013] Figure 4 shows a scanning electron microscope (SEM) image of the cathode material used in Comparative Example 1.

[0014] Figure 5 is a cyclic comparison diagram of Embodiment 1 and Comparative Examples 1-2 of this application.

[0015] Explanation of reference numerals in the attached diagram: 101 - Positive electrode; 102 - Negative electrode; 103 - Separator. Detailed Implementation

[0016] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0017] This application provides a cathode material. In the scanning electron microscope image of the cathode material, the average aspect ratio X / Y of the particles in the cathode material satisfies: 1≤X / Y≤1.6, where X is the length of the longest straight side of a single particle, and Y is the length of the straight side perpendicular to the midpoint of the longest straight side. After compaction under 6T pressure, the cathode material is characterized by laser particle size distribution. The volume percentage of particles smaller than 1μm in the cathode material is 2% to 4%.

[0018] First, this application controls the average aspect ratio X / Y of the particles in the cathode material to satisfy 1≤X / Y≤1.6. Within this range, the aspect ratio of the particles is relatively low. A lower aspect ratio helps reduce the stress difference between the length and radial directions of the particles during the rolling process, thereby reducing the breakage of the cathode material during electrode rolling and improving the gas generation performance problem caused by excessive active sites. Second, this application further controls the volume percentage of particles smaller than 1μm (defined as micropowder) in the cathode material to be 2%–4% after compaction under 6T pressure. The micropowder in the cathode material can fill the gaps between large particles (i.e., particles with a diameter greater than 1μm), thereby increasing the compaction density of the material. This improves the problem of increased gaps between particles after rolling caused by low aspect ratio particles, which leads to lower compaction density and narrower particle size distribution, resulting in a decrease in capacity. Therefore, while achieving a high volumetric energy density, it avoids excessively large active sites that could increase side reactions, thus improving the cycle performance and high-temperature storage performance of the cathode material.

[0019] Therefore, this application addresses the issue of reduced active sites, narrower particle size distribution, and decreased compaction density caused by particle size distribution in the cathode material within the aforementioned range during electrode preparation. This allows the micro-powder in the cathode material to fill the voids between larger particles, thereby increasing the material's compaction density. Simultaneously, it mitigates the capacity reduction caused by a particle aspect ratio in the range of 1–1.6. Furthermore, by controlling the compaction of the cathode material under 6T pressure, the volume percentage of particles smaller than 1μm in the cathode material is maintained at 2%–4%. This achieves a higher volumetric energy density while mitigating the problem of increased active sites and side reactions due to particle breakage.

[0020] For example, the average aspect ratio X / Y of the particles can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or any value within the range of any two of the above values. The volume percentage of particles smaller than 1 μm in the cathode material can be 2%, 2.5%, 3%, 3.5%, 4%, or any value within the range of any two of the above values. It should be noted that, using Nano Measure software, n particles that appear completely in the electron microscope images are randomly selected from 10 electron microscope images. The length M of the longest straight side of each particle and the length N of the straight side perpendicular to the midpoint of the longest straight side are measured. The average aspect ratio of the n particles is M / N, where n ≥ 50. It should be noted that a single-crystal particle appearing completely in the field of view of an electron microscope image means that the outline of the single-crystal particle is completely displayed in the electron microscope image, and the outline of the single-crystal particle is not covered by other single-crystal particles in the field of view or divided by the boundaries of the electron microscope image. It should also be noted that the longest straight edge refers to the diameter line within the circumcircle of the particle, whose two ends lie on the outline of the single-crystal particle. The straight edge perpendicular to the midpoint of the longest straight edge refers to a straight line that is perpendicular to the midpoint of the longest straight edge and whose two ends lie on the outline of the single-crystal particle.

[0021] Under 6T pressure, particles of 0–1 μm account for 10%–20% of the volume fraction of particles of 0–2 μm. By further controlling the volume fraction of 0–1 μm particles within this range, the compaction density of the material can be further improved. This further mitigates the problem of reduced small particles and fine powder caused by an aspect ratio of 1–1.6, resulting in a narrower particle size distribution in the cathode material and a lower compaction density, thus reducing capacity. For example, the volume fraction of 0–1 μm particles can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% of the volume fraction of 0–2 μm particles, or any value within any two of the above ranges. It should be noted that particles of 0–1 μm are defined as micro-powder, and particles of 1–2 μm are defined as small particles.

[0022] Therefore, this application aims to improve the long-term cycle performance, high-temperature storage performance, and gas generation performance of the cathode material by controlling the aspect ratio of the particles, the content of micronized powder in the cathode material, and the proportion of particles of different sizes, while ensuring that the material has good capacity and achieving the overall performance improvement of the cathode material.

[0023] In some embodiments, the proportion of particles satisfying 1≤X / Y≤1.6 in the cathode material is over 90%. By controlling the aspect ratio of over 90% of the particles in the material to be 1 to 1.6, it is beneficial to improve the overall roundness of the particles in the cathode material, thereby further reducing the specific surface area of ​​the cathode material, reducing the generation of side reactions, and thus further improving the long-term cycle performance, high-temperature storage performance, and gas generation performance of the cathode material.

[0024] In some embodiments, the specific surface area of ​​the cathode material is 0.4 m². 2 / g~0.8m 2 The cathode material has particles with a small aspect ratio, rounded shape, low powder content, and small specific surface area. This smaller specific surface area helps reduce direct contact between the cathode material and the electrolyte, thereby reducing side reactions and improving the long-term cycle performance, high-temperature storage performance, and gas generation performance of the cathode material. For example, the specific surface area of ​​the cathode material can be 0.4 m² / g. 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.8m 2 / g or any value within the range of any two of the above values.

[0025] In some embodiments, the cathode material can be a single-crystal cathode material, and the average particle size of a single particle in the cathode material can be 1 μm to 5 μm. For example, the average particle size of a single particle can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any value within the range of any two of the above values.

[0026] It is important to note that the difference between single-crystal cathode materials and polycrystalline cathode materials (i.e., polycrystalline secondary particles) lies in the fact that the smallest particles in polycrystalline secondary particles are formed by the agglomeration of nanoscale primary particles. In contrast, the smallest particles in single-crystal cathode materials are typically micrometer-sized single primary particles. Generally, in addition to EBSD testing, scanning electron microscopy (SEM) and other characterization methods can be used to determine whether the obtained cathode product is a single-crystal material. For example, for single-crystal cathode materials, SEM can characterize the morphology of single-crystal particles, showing that they are generally regular or irregular spherical in shape, with no significant particle agglomeration. EBSD can also characterize the orientation of single-crystal cathode materials. EBSD observation shows that at least one grain has the same color, indicating that at least one grain has the same orientation; grains with the same orientation are single crystals. It is important to clarify that the "single-crystal cathode material" known to those skilled in the art is not a "single crystal" in the strict crystallographic sense. In crystallography, an ideal single crystal refers to a crystal with completely identical arrangement and orientation. However, due to limitations imposed by impurities, strain, and crystal defects, ideal single crystals are extremely rare and difficult to produce in the laboratory. Therefore, the single-crystal cathode materials known in the art are actually more accurately described as "single-crystal morphology" cathode materials, differing only in size from polycrystalline materials composed of numerous small primary particles. For ease of understanding, the single-crystal cathode material described in this application can be understood as cathode material particles containing a single grain with the same orientation, and the average grain size of such a single grain being 1 μm to 5 μm.

[0027] Understandably, a single grain in this application can be a single particle composed of a primary particle. The aforementioned single-crystal cathode material may also contain a small number of "quasi-secondary particles" formed by the adhesion of several single particles. "Primary particle" refers to the smallest particle unit identified when observing cathode active materials using a scanning electron microscope. "Secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles, exhibiting a relatively rounded spherical morphology. "Quasi-secondary particles" are formed by the adhesion of several single particles. Typically, the particle size of a single particle in these quasi-secondary particles is between 1 μm and 5 μm, and generally, the roundness of "quasi-secondary particles" is lower than that of conventional "secondary particles."

[0028] It should be further clarified that the "single crystal" in "single crystal cathode material" as known to those skilled in the art is not a "single crystal" in the strict sense. In crystallography, an ideal single crystal refers to a crystal with completely identical arrangement and orientation. However, due to limitations caused by impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in a laboratory. Therefore, the single crystal cathode materials known in the art are actually more accurately described as "single crystal-like morphology" cathode materials, which differ from polycrystalline materials composed of numerous small primary particles only in size due to their large particle size resembling single crystals.

[0029] In some embodiments, the median particle size D50 of the cathode material is 2 μm to 6 μm. The median particle size D50 represents the particle size of the material when the cumulative particle size distribution percentage reaches 50% by volume. By controlling the median particle size of the cathode material within the above-mentioned appropriate range, this application achieves moderate particle size, which is beneficial for reducing the specific surface area of ​​the particles and minimizing side reactions between the particles and the electrolyte, thereby improving the safety and cycle life of the material. Simultaneously, particles within the above-mentioned size range also help reduce internal stress within the particles, reducing the risk of electrochemical polarization of lithium ions inside and outside the particles, thereby increasing the capacity of the cathode material. Exemplarily, the median particle size D50 of the cathode material is 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or any value within the range of any two of the above values.

[0030] In some embodiments, the ratio of (D90-D10) / D50 of the cathode material is ≤2. D10 represents the particle size corresponding to 10% of the cumulative particle size distribution, meaning that 10% of the particles in the particle group are smaller than this size. Typically, D10 is used to describe the finer particles in the particle group. D90 represents the particle size corresponding to 90% of the cumulative particle size distribution, meaning that 90% of the particles in the particle group are smaller than this size. D90 is typically used to describe the coarser particles in the particle group. (D90-D10) / D50 represents the width of the particle size distribution in the cathode material. By controlling (D90-D10) / D50 ≤ 2, this application ensures a moderate particle size distribution in the cathode material, reducing the specific surface area of ​​the particles without decreasing the compaction density of the material, thereby ensuring that the cathode material possesses excellent cycle performance, storage performance, and capacity. For example, the (D90-D10) / D50 of the cathode material can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any value within the range of any two of the above values.

[0031] In some embodiments, the powder compaction density of the cathode material is ≥3.0 g / cm³. 3 By controlling the aspect ratio of the particles in the material and simultaneously adjusting the proportion of micro-powder and small particles, the powder compaction density of the cathode material can be effectively improved. This ensures that the cathode material has a high compaction density when fabricated into an electrode sheet, thereby increasing the capacity of the cathode material. For example, the powder compaction density of the cathode material can be 3.0 g / cm³. 3 3.1g / cm 3 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 3.9g / cm 3 4g / cm 3 wait.

[0032] In some embodiments, the tap density of the cathode material is ≥1.5 g / cm³. 3 By adjusting the proportion of micro-powder and small particles in the cathode material, the tap density of the cathode material can be effectively improved, achieving a tap density of 1.5 g / cm³. 3 The above methods can increase the tap density of the electrode, thereby improving the battery capacity. For example, the tap density of the positive electrode material can be 1.5 g / cm³. 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2g / cm 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 2.5g / cm 3 wait.

[0033] In some embodiments, the pH of the cathode material is ≤12. By controlling the aspect ratio of the particles and the proportion of micronized powder and small particles, it is beneficial to increase the compaction density of the material while reducing the specific surface area of ​​the particles. Simultaneously, controlling the pH value of the cathode material within a suitable range can effectively improve its electrochemical activity and ensure the smooth diffusion of lithium ions within the material, thereby improving battery performance. For example, the pH of the cathode material can be 12, 11, 10, 9, 8, etc.

[0034] In some embodiments, the general formula of the positive electrode material is as follows: Li x Ni a Co b N c M dO2, N element includes at least one of Mn and Al, M element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, B, Ca, Nb, W, Sb, Ta, Sn and Y, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.35, 0≤d≤0.10, and a+b+c+d=1. By doping ternary cathode materials, the crystal structure of the cathode material can be optimized, the surface morphology of the particles can be further improved, and the structural stability and conductivity of the cathode material can be further enhanced.

[0035] This application also provides a method for preparing the aforementioned cathode material, specifically including the following steps:

[0036] Step S1: Add the first additive to the mixture of precursor and lithium salt and mix to obtain a mixture, and pre-sinter the mixture to obtain a pre-sintered product.

[0037] The pre-sintering process is carried out in an oxygen or air atmosphere, enabling the material to react with oxygen to form the target layered compound.

[0038] In some embodiments, during the pre-sintering process, the pressure inside the reactor is controlled within the range of 20 Pa to 60 Pa, the pre-sintering temperature can be 500 to 900 °C, and the sintering time can be 2 to 8 hours. Controlling the sintering furnace pressure and temperature allows the lithium salt to be fully embedded in the precursor, reducing lithium salt residue. Simultaneously, during the pre-oxidation sintering process, the microparticles can undergo a certain degree of pre-fusion, controlling the aspect ratio of the particles, making the particles more rounded, and reducing microparticles on the material surface. Exemplarily, the pre-sintering temperature can be any value within the range of 500 °C, 600 °C, 700 °C, 800 °C, 900 °C, or any two of these values; the pre-sintering time can be any value within the range of 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or any two of these values.

[0039] In some embodiments, a pore-forming agent may be added to the mixture, wherein the mass of the pore-forming agent accounts for 3% to 10% of the precursor mass. Since the material needs to react with oxygen to form the target layered compound during sintering, it is difficult for oxygen to completely penetrate the mixture. Therefore, a pore-forming agent is added during sintering. The pore-forming agent completely decomposes at high temperatures without significant residue or impurities. Simultaneously, the decomposition of the pore-forming agent produces gas, which forms pores inside the mixture upon exhaust. These pores facilitate oxygen penetration, thereby allowing the material inside the mixture to react fully, reducing lithium residue, reducing micropowder residue on the material surface, and further controlling particle size. Exemplarily, the mass of the pore-forming agent accounts for any value within the range of 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any two of the above values ​​of the cathode material precursor mass.

[0040] In some embodiments, the pore-forming agent may include at least one of starch, pine powder, polyvinyl alcohol, polyethylene glycol, coal powder, and lithium peroxide.

[0041] In some embodiments, the general formula of the cathode material precursor can be Ni. a Co b N c (OH)2 or LiNi a Co b N c O2, where a+b+c=1; 0.5≤a≤0.98, 0≤b≤0.20, 0≤c≤1-ab. The first additive may include lithium salt and dopant, wherein the dopant may include at least one compound selected from Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, and Y, and the lithium salt may be at least one selected from LiOH and Li2CO3. The selection of the first additive varies depending on the type of cathode material precursor, but the first additive must contain at least a lithium salt.

[0042] In some embodiments, the ratio of the molar amount of Li to the total molar amount of other metal elements in the pre-sintered product can be 0.98 to 1.10.

[0043] In some embodiments, the first additive may include at least one of TiO2, AlOOH, WO3, ZrO2, Y2O3, NbO2, etc.

[0044] Step S2: The pre-sintered product is sintered once to obtain the cathode material matrix.

[0045] The single sintering process comprises a first sintering stage and N second sintering stages performed sequentially. The temperature of each second sintering stage is lower than that of the first sintering stage, and the temperature gradient across the N second sintering stages decreases with the number of sintering stages, where N is an integer greater than or equal to 1. In other words, the single sintering process is a multi-gradient sintering process, including a high-temperature first sintering stage and multiple low-temperature second sintering stages, with the temperature gradient of different second sintering stages decreasing as the number of sintering stages increases.

[0046] In some embodiments, the temperature T2 of the first sintering stage is 800–1000°C, and the time is 2–6 hours. For example, the temperature of the first sintering stage can be any value within the range of any two values ​​of 800°C, 850°C, 900°C, 950°C, 1000°C, or higher; the sintering time can be any value within the range of any two values ​​of 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or higher.

[0047] In some embodiments, the average heating rate of the first sintering stage is ≤5℃ / min. Exemplarily, the heating rate can be any value within the range of 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, or any two of the above values.

[0048] In some embodiments, the temperature of each second sintering stage is T2-n×ΔT, and the time is 2 to 6 hours, where n is the order of the second sintering stage in N second sintering stages, n is an integer greater than or equal to 1, and ΔT can be 20 to 40°C. For example, ΔT can be any value within the range of any two values ​​of 20°C, 30°C, 40°C, or above.

[0049] In some embodiments, a single sintering process may include three gradient sintering stages, i.e., N equals 2. In this case, the temperature T3 of the first second sintering stage may be T2-ΔT, and the sintering time may be 2 to 4 hours. The temperature T4 of the second second sintering stage may be T2-2×ΔT, and the sintering time may be 2 to 6 hours.

[0050] In some embodiments, the total sintering time for a single sintering can be 6 to 16 hours. For example, the total sintering time can be any value within the range of 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, or any two of the above values.

[0051] The pressure inside the reactor is 20 Pa to 60 Pa, and the temperature is 800 to 1000 °C for 2 to 6 hours. This high-temperature sintering process allows for the initial fusion of the pre-sintered product and the micropowder, resulting in more rounded particles and achieving control over the particle aspect ratio, particle size, and micropowder content. Subsequently, sintering is carried out at a temperature of T2-ΔT for 2 to 4 hours. Continuing sintering at a slightly lower temperature further fuses the pre-sintered product and micropowder, preventing excessive particle growth due to high temperatures, thus facilitating further control over the particle aspect ratio and particle size. Finally, the temperature is further reduced to T2-2×ΔT for 2 to 6 hours to achieve even greater fusion of the pre-sintered product and micropowder, while simultaneously further controlling the particle aspect ratio and particle size. This step first achieves lithium-ion intercalation and initial particle growth through high-temperature sintering, followed by two stages of low-temperature sintering, which further enables lithium-ion intercalation and also serves to anneal and repair micrograin boundaries. By controlling the temperature and reaction time of particle fusion, the aspect ratio, particle size, and micron powder content of single crystal particles can be effectively controlled. In addition, the total sintering time of the three sintering stages does not exceed 16 hours, which can keep the size of the single crystal particles within a suitable range to prevent excessive crystal growth.

[0052] Understandably, steps S1 and S2 can also be combined to form multi-gradient sintering by controlling the temperature and time of different sintering stages.

[0053] Step S3: The cathode material matrix is ​​crushed, and the aspect ratio of the single crystal particles in the obtained cathode material matrix satisfies: 1≤X / Y≤1.6. After compaction under 6T pressure, the volume ratio of particles smaller than 1μm in the cathode material matrix is ​​found to be 2% to 4% by Malvern 3000 particle size analyzer.

[0054] Through the aforementioned pre-sintering and primary sintering processes, the aspect ratio, particle size, and micron content of single-crystal particles can be controlled, and a cathode material matrix that meets the above requirements can be obtained after pulverization.

[0055] In some embodiments, particles of 0–1 μm in the cathode material matrix account for 10%–20% of the volume fraction of particles of 0–2 μm.

[0056] Step S4: The pulverized positive electrode material matrix is ​​mixed with the second additive and then sintered a second time to obtain the evidence material.

[0057] Specifically, the qualified cathode material matrix that meets the conditions in step S3 is sintered a second time with a second additive in an oxygen atmosphere. The second additive includes at least one compound selected from B, Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, and Y. The second additive serves as a coating agent, and the second sintering is a low-temperature sintering process. The purpose is to uniformly coat the cathode material matrix with the coating agent for surface modification, thereby further improving the structural stability and electrochemical performance of the cathode material. This process has no significant impact on the particle size or aspect ratio of the cathode material. Understandably, the particle size of the cathode material can well inherit the particle size of the matrix, and the subsequent coating process has minimal impact on the particle size of the matrix.

[0058] In some embodiments, the secondary sintering temperature can be 500–900°C, the sintering time can be 6–16 h, and the average heating rate is ≤5°C / min. By controlling the temperature, time, and heating rate of the secondary sintering, the second additive can be uniformly coated on the surface of the substrate, further optimizing the surface structure of the cathode material and thus further improving the structural stability and electrical performance of the cathode material. For example, the secondary sintering temperature can be any value within the range of 500°C, 600°C, 700°C, 800°C, 900°C, or any two of the above values; the secondary sintering time can be any value within the range of 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, or any two of the above values.

[0059] The cathode material and its preparation method provided in this application aim to improve the long-term cycle performance, high-temperature storage performance, and gas generation performance of the cathode material by controlling the aspect ratio of the particles, the content of micronized powder, and the proportion of particles of different sizes, while ensuring good capacity and achieving an overall improvement in the performance of the cathode material. Specifically, the aspect ratio X / Y of the particles is controlled to satisfy 1 ≤ X / Y ≤ 1.6. Particles within this range have a low aspect ratio, resulting in higher roundness. Increased roundness helps reduce the specific surface area of ​​the cathode material, which in turn reduces direct contact between the cathode material and the electrolyte, thereby reducing side reactions and improving the long-term cycle performance, high-temperature storage performance, and gas generation performance of the cathode material. Furthermore, by further controlling the volume percentage of particles smaller than 1 μm in the cathode material to 2%–4%, on the one hand, side reactions between the cathode material and the electrolyte can be reduced during the charging and discharging process of the battery, reducing gas production and thus further improving the cycle life and high-temperature storage performance of the cathode material; on the other hand, during the preparation of the electrode sheet, the micro-powder in the material can fill the gaps between large particles, thereby increasing the compaction density of the material and mitigating the problem of reduced micro-powder quantity, narrower particle size distribution, and lower compaction density caused by the average aspect ratio of the particles being in the range of 1–1.6, which leads to a decrease in capacity. Therefore, it is possible to obtain a high volumetric energy density without causing uncontrolled specific surface area and increasing side reactions.

[0060] This application also provides a positive electrode sheet using the aforementioned positive electrode material, including a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes the aforementioned positive electrode material.

[0061] The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, the current collector formed by combining the aforementioned conductive foil and polymer substrate.

[0062] This application also provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, an electrode assembly, and an electrolyte / electrolyte. Both the electrode assembly and the electrolyte / electrolyte are located within the casing. The electrode assembly includes a separator, a negative electrode, and the aforementioned positive electrode, with the separator disposed between the positive and negative electrode.

[0063] In some embodiments, the outer casing can be a packaging bag sealed with an encapsulating film (such as an aluminum-plastic film), for example, the secondary battery is a pouch battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0064] In some embodiments, the electrode assembly may be a stacked structure, which is formed by alternating layers of a positive electrode, a separator, and a negative electrode. In other embodiments, the electrode assembly may also be a wound structure, which is formed by winding a positive electrode, a separator, and a negative electrode after they are stacked in sequence.

[0065] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a layer of negative electrode active material disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more. The battery provided in this application embodiment has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., and there is no limitation here.

[0066] Figures 1 and 2 illustrate the lithium delithiation and lithium insertion processes during charging and discharging of a lithium-ion battery prepared using the positive electrode material provided in the embodiments of this application. As shown in Figure 1, when the lithium-ion battery is charging, lithium ions are delithilated from the positive electrode 101, pass through the electrolyte and the separator 103, and are inserted into the negative electrode 102. As shown in Figure 2, when the lithium-ion battery is discharging, lithium ions are delithilated from the negative electrode 102, pass through the electrolyte and the separator 103, and are inserted back into the positive electrode 101.

[0067] This application embodiment uses the aforementioned cathode material to prepare a secondary battery. By controlling the aspect ratio X / Y of the particles in the cathode material to satisfy: 1 ​​≤ X / Y ≤ 1.6, after compaction under 6T pressure, the volume percentage of particles smaller than 1μm in the cathode material is 2% to 4%. This improves the battery's long-term cycle performance, high-temperature storage performance, and gas generation performance while ensuring good battery capacity, thus achieving an overall performance improvement. Specifically, when the aforementioned cathode material is used in a coin cell, the battery's cycle performance is evaluated, and the retention rate after 50 cycles at room temperature is ≥93%.

[0068] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the present application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically mentioned are all conventional commercially available products or open-source materials.

[0069] Example 1:

[0070] Step S1, weigh out the sample with the general chemical formula Ni 0.6 Co 0.1 Mn 0.3 2.5 kg of (OH)2 precursor was added to 1.25 kg of LiOH·H2O, 3000 ppm of ZrO2, 1000 ppm of Al2O3 and 1000 ppm of Sr(OH)2 and mixed in a high-speed mixer for 40 min to obtain a mixture.

[0071] Step S2: The aforementioned mixture is sintered for 6 hours in an oxygen or air atmosphere at a furnace pressure of 50 Pa and a temperature of T1 = 700 °C to obtain a pre-sintered product.

[0072] Step S3: The pre-sintered product is sintered in an oxygen or air atmosphere at a furnace pressure of 50 Pa and a temperature of 960℃ for 4 hours at T2. The heating rate in the T2 stage is 3℃ / min. The product is then sintered at 940℃ for 6 hours at T3 and 920℃ for 4 hours at T4 to obtain the cathode material matrix.

[0073] Step S4: The obtained cathode material matrix is ​​crushed. The aspect ratio of the crushed cathode material matrix is ​​measured under an electron microscope at 3K magnification. When the aspect ratio of the matrix satisfies 1≤X / Y≤1.6, and after compaction under 6T pressure, the volume percentage of microparticles smaller than 1μm in the matrix is ​​found to be 2% to 4% using a Malvern 3000 particle size analyzer, the cathode material matrix will continue to undergo subsequent processing.

[0074] Step S5: The pulverized cathode material matrix that meets the requirements is mixed with 2000ppm WO3 and 1000ppm TiO2, and the mixture is placed in a crucible and sintered at 600℃ for 8 hours in an oxygen atmosphere with a heating rate of 3℃ / min to obtain the cathode material.

[0075] Example 2

[0076] The difference from Example 1 is that in step S1, the general formula of the precursor is Ni. 0.5 Co 0.2 Mn 0.3 (OH)2. The other steps are basically the same as in Example 1; please refer to Example 1.

[0077] Example 3

[0078] The difference from Example 1 is that in step S1, the general formula of the precursor is Ni. 0.7 Co 0.1 Mn 0.2 (OH)2. The other steps are basically the same as in Example 1; please refer to Example 1.

[0079] Example 4

[0080] The difference from Example 1 is that in step S2, the mixture is sintered for 8 hours in an oxygen or air atmosphere at a furnace pressure of 50 Pa and a temperature of T1 = 700°C to obtain a pre-sintered product. The other steps are basically the same as in Example 1; please refer to Example 1.

[0081] Example 5

[0082] The difference from Example 1 is that in step S1, a substance with the chemical formula Ni is weighed. 0.6 Co 0.1 Mn 0.3 2.5 kg of (OH)2 precursor was added to 1.25 kg of lithium salt (LiOH·H2O), along with 3000 ppm of ZrO2, 1000 ppm of Al2O3, 1000 ppm of Sr(OH)2, and 500 ppm of WO3. The mixture was then mixed in a high-speed mixer for 40 min to obtain the final mixture.

[0083] In step S2, the aforementioned mixture is sintered for 2 hours in an oxygen or air atmosphere at a furnace pressure of 50 Pa and a temperature of T1 = 700 °C to obtain a pre-sintered product.

[0084] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0085] Example 6

[0086] The difference from Example 1 is that in step S3, the pre-sintered product is sintered in an oxygen or air atmosphere at a furnace pressure of 50 Pa, at a temperature of 960°C for 6 hours at T2, 940°C for 6 hours at T3, and 920°C for 4 hours at T4 to obtain the cathode material matrix.

[0087] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0088] Example 7

[0089] The difference from Example 1 is that in step S3, the pre-sintered product is sintered in an oxygen or air atmosphere at a furnace pressure of 50 Pa, at temperature T2 of 960°C for 2 hours, at temperature T3 of 940°C for 6 hours, and at temperature T4 of 920°C for 4 hours to obtain the cathode material matrix. Other steps are basically the same as in Example 1; please refer to Example 1.

[0090] Example 8

[0091] The difference from Example 1 is that in step S3, the pre-sintered product is sintered in an oxygen or air atmosphere at a furnace pressure of 50 Pa, at a temperature of 980°C for 2 hours, at a temperature of 940°C for 8 hours, and at a temperature of 900°C for 4 hours to obtain the cathode material matrix.

[0092] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0093] Example 9

[0094] The difference from Example 1 is that in step S3, the pre-sintered product is sintered in an oxygen or air atmosphere at a furnace pressure of 50 Pa, at a temperature of 980°C for 2 hours, at a temperature of 950°C for 8 hours, and at a temperature of 920°C for 4 hours to obtain the cathode material matrix.

[0095] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0096] Example 10

[0097] The difference from Example 1 is that in step S1, the lithium salt is anhydrous lithium hydroxide (LiOH).

[0098] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0099] Example 11

[0100] The difference from Example 1 is that in step S1, an additional 3% of lithium peroxide by mass of the precursor is added to the mixture as a pore-forming agent.

[0101] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0102] Example 12

[0103] The difference from Example 1 is that in step S3, the pre-sintered product is sintered in an oxygen or air atmosphere at a furnace pressure of 50 Pa, at a temperature of 970°C for 2 hours, at a temperature of 950°C for 8 hours, and at a temperature of 930°C for 4 hours to obtain the cathode material matrix.

[0104] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0105] Example 13

[0106] The difference from Example 1 is that in step S1, a substance with the chemical formula Ni is weighed. 0.6 Co 0.1 Mn 0.3 2.5 kg of O2 precursor, 1.25 kg of LiOH·H2O, 3000 ppm of ZrO2, 1000 ppm of Al2O3 and 1000 ppm of Sr(OH)2 were added and mixed in a high-speed mixer for 40 min to obtain a mixture.

[0107] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0108] Example 14

[0109] The difference from Example 1 is that in step S1, a substance with the chemical formula Ni is weighed. 0.6 Co 0.1 Al 0.3 2.5 kg of (OH)2 precursor, 1.25 kg of LiOH·H2O, 3000 ppm of ZrO2, 1000 ppm of Al2O3 and 1000 ppm of Sr(OH)2 were added and mixed in a high-speed mixer for 40 min to obtain a mixture.

[0110] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0111] Comparative Example 1

[0112] The difference from Example 1 is that in step S3, the sintering time of T2 is 2h, the heating rate is 3℃ / min, and the sintering time of T3 is 4h.

[0113] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0114] Comparative Example 2

[0115] The difference from Example 1 is that in step S3, the sintering time of T2 is 6h, the heating rate is 6℃ / min, and the sintering time of T3 is 8h.

[0116] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0117] Comparative Example 3

[0118] The difference from Example 1 is that in step S3, only one high-temperature sintering is performed, the sintering time of T2 is 12h, the heating rate is 3℃ / min, and the subsequent low-temperature sintering of T3 and T4 is not performed.

[0119] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0120] Comparative Example 4

[0121] The difference from Example 1 is that in step S3, only one high-temperature sintering is performed, with a sintering temperature T2 of 960°C, a sintering time T2 of 8 hours, and a heating rate of 3°C / min. The subsequent low-temperature sintering in T3 and T4 is not performed.

[0122] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0123] Comparative Example 5

[0124] The difference from Example 1 is that in step S3, the pre-sintered product is sintered in an oxygen or air atmosphere at a furnace pressure of 50 Pa, at a temperature of 960°C for 2 hours at T2, at a temperature of 900°C for 8 hours at T3, and at a temperature of 850°C for 2 hours at T4 to obtain the cathode material matrix.

[0125] The other steps are basically the same as in Example 1, please refer to Example 1. The pre-sintered product is sintered in an oxygen or air atmosphere, with a furnace pressure of 50 Pa, at a temperature T2 of 960°C for 4 hours, a heating rate of 3°C / min in the T2 stage, at a temperature T3 of 940°C for 6 hours, and at a temperature T4 of 920°C for 4 hours to obtain the cathode material matrix.

[0126] Comparative Example 6

[0127] The difference from Example 1 is that in step S3, only one high-temperature sintering is performed, with a sintering temperature T2 of 970°C, a sintering time of 12 hours, and a heating rate of 3°C / min. The subsequent low-temperature sintering steps T3 and T4 are not performed.

[0128] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0129] The performance of the cathode materials obtained in Examples 1-14 and Comparative Examples 1-6 were tested using the following methods.

[0130] 1. Length-to-diameter ratio test:

[0131] Sample preparation: Take the pulverized positive electrode material and use a 0.5mm long conductive adhesive to pick up the material. After picking up the material, use a rubber bulb to blow the conductive adhesive surface with the material 10 times.

[0132] Electron microscopy: Scanning electron microscope (SEM) was used to conduct the test under an electron beam of 5kV / 10mA. At least 10 electron micrographs were taken at a magnification of 3K for the selected scenes with more particles.

[0133] Aspect Ratio Test: Using Nano Measure software, n particles that appear completely within the electron microscope images were randomly selected from 10 images. The length M of the longest straight side and the length N of the straight side perpendicular to the midpoint of the longest straight side were measured for each particle. The average aspect ratio of the n particles is M / N, where n ≥ 50. It should be noted that a single-crystal particle appearing completely within the field of view of the electron microscope image means that the outline of the single-crystal particle is fully displayed in the image, and its outline is not covered by other single-crystal particles in the field of view or divided by the boundaries of the electron microscope image. It should also be noted that the longest straight side refers to the diameter line within the circumcircle of the particle whose ends lie on the outline of the single-crystal particle. The straight side perpendicular to the midpoint of the longest straight side refers to a straight line perpendicular to the midpoint of the longest straight side and whose ends lie on the outline of the single-crystal particle.

[0134] 2. Micron powder quantity test:

[0135] Sample preparation: Place the pulverized positive electrode material matrix into the mold and press it for 10 minutes using a pressure of 6t. After pressing, remove the matrix from the mold and grind the resulting block using an agate mortar and pestle for 1 minute to disperse the material.

[0136] Measurement: The particle size of the ground material was measured using a Malvern 3000 laser particle size analyzer. The percentage of accumulated particles smaller than 1 μm and the percentage of accumulated particles smaller than 2 μm were recorded. Specifically, the ground material was poured into pure water and ultrasonically dispersed for 30 seconds at a power of 240 W. Then, an appropriate amount of sodium hexametaphosphate was added to the dispersed sample, stirred evenly, and poured into the sample cell of the testing equipment. After waiting for 10 seconds, the sample testing was started.

[0137] 3. Powder compaction density test:

[0138] Using a Carver 4350 testing instrument from the United States, 1g of powder sample was placed into a mold and pressed with a pressure of 3T for 30s. After pressing, the height was measured and the compaction density was calculated.

[0139] 4. Specific surface area test: The specific surface area of ​​the material was tested using the McMeter 3020 nitrogen adsorption method.

[0140] Specifically, the total mass of the empty sample tube is weighed as m1; 3g (±0.005) of sample is added to the sample tube; the sample tube after adding the sample is evacuated and degassed at 300℃ for 1 hour, and after cooling, the total mass of the sample tube and the sample is weighed as m2; the sample mass m = m2 - m1. The sample tube is placed in liquid nitrogen, and the nitrogen adsorption capacity V of the sample is measured at 6 relative pressures P / P0 to obtain adsorption isotherms; where P / P0 is set to 0.05 / 0.1 / 0.15 / 0.20 / 0.25 / 0.30. The monolayer saturated adsorption capacity Vm is obtained from the adsorption isotherms, and the specific surface area of ​​the cathode material is calculated based on Vm.

[0141] 5. Tap density test:

[0142] The American CANTA DAT-4-220 tap density meter was used.

[0143] The testing procedure includes: cleaning the graduated cylinder and weighing it (mL); adding the sample into the graduated cylinder, ensuring the sample surface is as horizontal as possible, and wiping the surrounding area with a paper towel; weighing the total mass of the sample and graduated cylinder (m2); placing the graduated cylinder on the vibration stage and securing it with three symmetrical feet; turning on the instrument and activating the vibration switch; the instrument will automatically stop after vibrating a specified number of times; removing the graduated cylinder and reading the sample volume. If the sample surface is horizontal after vibration, read the volume directly; if it is oblique, take the average of the readings at the highest and lowest points (V).

[0144] Calculation formula: Tap density = (m2-m1) / V.

[0145] 6. pH test:

[0146] Using a Mettler FE28 electrode, 5g of the positive electrode material sample was taken, and an appropriate amount of pure water was added. After sonication for 10 minutes, the sample was removed and allowed to stand for 15 minutes. After pH meter calibration, the composite electrode was inserted into the supernatant solution to be tested. The pH value of the solution was calculated based on the potential difference between the measuring electrode and the reference electrode.

[0147] 7. Battery manufacturing and performance testing:

[0148] a. Sample preparation for electrochemical performance testing:

[0149] Button cell fabrication: The electrochemical performance of the prepared positive electrode material was evaluated using button half-cells. The specific method is as follows: The positive electrode material, SP, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 93:5:2. NMP was added at a solid content of 50%, and the mixture was prepared into a viscous slurry using a high-speed disperser. The slurry was then evenly coated onto aluminum foil with a scraper, dried in an oven at 80°C, and rolled to form positive electrode sheets with a diameter of 14 mm. A 16 mm diameter lithium sheet was used as the negative electrode sheet, Celgard polyethylene PP film was used as the separator, and a 1 mol / L LiPF6 carbonate solution (DEC / EC volume ratio 1:1) was used as the electrolyte. The lithium-ion battery was assembled according to the industrial CR2025 button cell assembly method in an argon-filled glove box, where the oxygen and moisture content were controlled below 0.5 ppm. At a temperature of 25℃±1℃, the voltage range for charge-discharge cycles is 3.0V to 4.4V, and the initial charge-discharge current is 0.1C (20mAh / g).

[0150] b. Button test:

[0151] Capacity test: The battery is placed at 3.0 to 4.4V and charged and discharged at a rate of 0.1C / 0.1C to test the capacity in the first week.

[0152] Cyclic testing: The battery was placed in a constant temperature chamber at 25°C and charged and discharged 50 times at a rate of 0.5C / 1C to obtain the cycle performance data.

[0153] The test results of the cathode materials of Examples 1-14 and Comparative Examples 1-6 are shown in Tables 1 and 2 below.

[0154] Table 1

[0155] Table 2

[0156] Examples 1-3 adjusted the Ni content in the precursor. For ternary cathode materials with different nickel contents, the preparation method of the embodiments of this application can ensure that the aspect ratio of the single crystal particles in the cathode material is in the range of 1 to 1.6 (specifically 1.3), the particles are relatively round, and the proportion of micro powder is low (3%). The volume fraction of small particles of 0 to 1 μm to large particles of 0 to 2 μm is low (15%). Single crystal cathode materials that meet the above conditions have good capacity and cycle performance.

[0157] Compared to Example 1, Example 4 further extends the pre-oxidation time, which is conducive to the full insertion of lithium, reduces residual lithium and fine powder, and repairs the grain boundaries of the material, thereby further improving the roundness of the single crystal particles. The resulting single crystal particles have an aspect ratio of 1 and are more spherical.

[0158] Compared to Example 1, the first additive in Example 5 increased W and shortened the pre-sintering time, resulting in a larger aspect ratio but lower roundness than in Example 1. This indicates that the length of the pre-sintering time affects the aspect ratio of the single crystal particles.

[0159] Compared to Example 1, Example 6 extended the sintering time of the first stage in step S3, increased the reaction time for particle fusion, and further reduced the content of micro powder (to 2%).

[0160] Compared to Example 1, Example 7 shortened the first-stage sintering time in step S3, shortened the reaction time for particle fusion, and increased the content of micro powder (to 4%).

[0161] Compared to Example 1, Examples 8-9 adjusted the temperature and time of the secondary sintering, which can control the content of micro powder and the aspect ratio of the particles.

[0162] Compared to Example 1, Example 10 used anhydrous lithium hydroxide (LiOH) and the same preparation method of this application was used. The resulting cathode material still met the requirements for particle size and micron content.

[0163] Compared to Example 1, Example 11, by adding a pore-forming agent, can further allow oxygen to fully enter the interior of the precursor mixture, so that the reaction can proceed fully, which is beneficial to improving the capacity and cycle performance of the cathode material.

[0164] Compared to Example 1, Example 12 increased the sintering temperature in step S3, shortened the high-temperature sintering time T2, and extended the low-temperature sintering time T3. The proportion of micro powder remained almost unchanged (3%), but the volume fraction of 0-1 μm particles to 0-2 μm particles decreased (to 6%), indicating that the particles underwent further fusion.

[0165] Compared to Example 1, the precursor of Example 14 is a nickel cobalt aluminum hydroxide precursor. Using the same preparation method of this application, the obtained cathode material still meets the range of particle size and micro powder content, and has high capacity and excellent cycle performance.

[0166] As can be seen from Examples 1-14 of this application, the prepared cathode materials all meet the requirement that the aspect ratio of single crystal particles is 1 to 1.6. At the same time, after being compacted under 6T pressure, the volume percentage of micro powders smaller than 1μm in the matrix is ​​2% to 4% as determined by a Malvern 3000 particle size analyzer. Cathode materials that meet the above conditions all have high capacity and excellent cycle performance.

[0167] Compared to Example 1, Comparative Examples 1-3 adjusted the sintering stage, temperature, and time of the secondary sintering. The resulting cathode materials had a large aspect ratio (1.7) for single crystal particles and a high content of micronized powder (at least 8%), leading to poor capacity and cycle performance. Comparative Example 4, compared to Example 1, only high-temperature sintering was performed in the primary sintering step, shortening the particle fusion time. The micronized powder content was high (18%), resulting in insufficient particle growth and a small aspect ratio (1.2), leading to poor cycle performance. Comparative Example 5, compared to Example 1, had a large gradient difference in the gradient sintering step and a shorter high-temperature sintering time, while the low-temperature sintering temperature was lower. At this temperature, the micronized powder content was suitable, but the particle aspect ratio was large (1.7), resulting in poor particle roundness and a large specific surface area, leading to poor cycle performance. Compared with Example 1, Comparative Example 6 only performed high-temperature sintering in the single sintering step, and the high-temperature sintering temperature was relatively high, which promoted particle fusion. Although the aspect ratio of the particles was suitable, the content of micro powder was too low (1%), the compaction density of the material was low, and the capacity of the obtained cathode material was low.

[0168] In addition, Figure 3 is a SEM image of the cathode material of Example 1. As can be seen from Figure 3, the aspect ratio of the single crystal particles in the cathode material of Example 1 is 1.3, the single crystal particles are round, and the proportion of micro powder in the cathode material is 3%. Figure 4 is a SEM image of the cathode material of Comparative Example 1. As can be seen from Figure 4, the aspect ratio of the single crystal particles in the cathode material of Comparative Example 1 is 1.7, the particles are not round enough, the specific surface area is large, and the proportion of micro powder is relatively large (reaching 10%). Figure 5 is a cycle comparison diagram of Example 1 and Comparative Examples 1-2. As can be seen from Figure 5, the cycle performance of Comparative Examples 1-2 is significantly worse than that of Example 1, which further proves that the cathode material prepared by the preparation method of this application can meet the requirements of particle size and micro powder content, thereby effectively improving the capacity and cycle performance of the cathode material.

[0169] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A positive electrode material, characterized in that, In the scanning electron microscope image of the cathode material, the average aspect ratio X / Y of the particles in the cathode material satisfies: 1≤X / Y≤1.6, where X is the length of the longest straight side of a single particle, and Y is the length of the straight side perpendicular to the midpoint of the longest straight side; after compaction under 6T pressure, the volume ratio of particles smaller than 1μm in the cathode material is 2% to 4%.

2. The cathode material according to claim 1, characterized in that, The cathode material satisfies any one of the following conditions: (1) X / Y is any value within the range of 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 or any two of these values; (2) 1 ≤ X / Y ≤ 1.3; (3) 1.1≤X / Y≤1.

5.

3. The cathode material according to claim 1, characterized in that, The cathode material satisfies any one of the following conditions: (1) After compaction under 6T pressure, the volume percentage of particles smaller than 1μm in the cathode material is 2%, 2.5%, 3%, 3.5%, 4% or any two of these values. (2) After compaction under 6T pressure, the volume ratio of particles smaller than 1μm in the cathode material is 2% to 3%; (3) After compaction under 6T pressure, the volume ratio of particles smaller than 1μm in the cathode material is 3% to 4%.

4. The cathode material according to claim 1, characterized in that, After compaction under 6T pressure, the 0-1μm particles in the cathode material account for 10%-20% of the volume fraction of the 0-2μm particles.

5. The cathode material according to claim 1, characterized in that, The proportion of particles satisfying 1≤X / Y≤1.6 in the cathode material shall not be less than 90%.

6. The cathode material as described in claim 1, characterized in that, The general formula of the cathode material is as follows: Li x Ni a Co b N c M d O2, N element includes at least one of Al and Mn, M element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, B, Ca, Nb, W, Sb, Ta, Sn, Y, where 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.35, 0≤d≤0.10, and a+b+c+d=1.

7. The positive electrode material as described in claim 1, characterized in that, The cathode material satisfies at least one of the following characteristics: (1) The cathode material is a single-crystal cathode material; (2) The cathode material is a single crystal material.

8. The cathode material as described in claim 1, characterized in that, In the scanning electron microscope image of the cathode material, the average particle size of the particles in the cathode material is 1 μm to 5 μm.

9. The positive electrode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following characteristics: (1) The volume median particle size D50 of the cathode material is 2μm to 6μm; (2) The volumetric particle size distribution width of the cathode material is: (D90-D10) / D50≤2.

10. The cathode material as described in claim 1, characterized in that, The specific surface area of ​​the positive electrode material is 0.4 m². 2 / g~0.8m 2 / g.

11. The cathode material as described in claim 1, characterized in that, The pH of the positive electrode material is ≤12.

12. The cathode material as described in claim 1, characterized in that, The compaction density of the positive electrode material is ≥3.0 g / cm³. 3 .

13. The cathode material as described in claim 1, characterized in that, The tap density of the positive electrode material is ≥1.5 g / cc.

14. A positive electrode plate, characterized in that, Includes the cathode material as described in any one of claims 1 to 13.

15. A secondary battery, characterized in that, It includes the positive electrode material as described in any one of claims 1 to 13 or the positive electrode sheet as described in claim 14.

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